Wells drilled in low-permeability subterranean formations are often treated by reservoir stimulation techniques, such as hydraulic fracturing, to increase hydrocarbon production rate. High viscosity fluids may be employed to carry proppant down-hole to prop open fractures in the formation. Known linear gels (water containing a gelling agent only) that can be operated at ambient temperature at the surface generally do not exhibit a sufficiently high viscosity to transfer proppant of a large size or large quantity. Consequently, crosslinkers may be used to increase fluid viscosity, providing adequate transport of larger proppant sizes or larger proppant quantity. Higher viscosity fluids also create wider fractures within the formation.
Guar and guar derivatives are among the most oft used polymers in hydraulic fracturing treatment. Guar derivatives, such as carboxymethyl guar (CMG) and carboxymethyl hydroxypropyl guar (CMHPG), are predominantly used in wells with a high bottom-hole temperature (BHT). In recent years, significant price increases in guar and supply shortages of guar have posed challenges for service companies and operators. Consequently, prices for guar derivatives have also increased. Interest in cellulose derivatives has increased for fracturing treatment due to the natural abundance of cellulose. However, known systems for incorporating cellulose derivatives crosslink the polymers only in a low pH environment. Also, known systems for using cellulose derivatives are limited to applications in which formation temperature is less than 250° F. due to rapid acid hydrolysis at higher temperatures.
In addition, fluid volumes in fracturing treatments have increased substantially, while public concern for water use and disposal has also increased. Rather than paying to treat and dispose of produced and flowback water, service companies and operators have pursued recycling in subsequent stimulation operations. “Produced water” refers to water generated from hydrocarbon wells. Generally the term is used in the oil industry to describe water that is produced along with oil and/or gas. “Flowback water” is a subcategory of produced water referring to fracturing fluid that flows back through the well, which may account for some fraction of the original fracture fluid volume.
Produced water, especially from shale plays such as Marcellus and Bakken, is known for its high total dissolved solids (TDS) and high divalent cation content. TDS and divalent cations pose challenges for known guar- and guar derivative-based fracturing fluids. Consequently, produced water intended for recycling in subsequent stimulation operations is treated to obtain a water quality suitable for the fracturing fluids. Even so, such treatment is often cost-prohibitive and time-consuming. Accordingly, other fluids suitable for higher formation temperatures, recycling of produced water, or both are desirable.